Aerospace vehicles typically require lightweight structural members that maximize payload carrying capacity and mission capabilities. For example, launch and space exploration vehicles often make use of composite materials in areas such as heat shields, nose cones and payload fairings in order to reduce weight while satisfying performance requirements. In order to further reduce vehicle weight, additional components such as cryogenic fuel tanks used to store pressurized propellants may be fabricated from composite materials. However, the use of composite materials for fuel tanks is challenging because of the severe environmental conditions to which the components of the tank may be subjected, as well as possible chemical incompatibilities, the cryogenic temperatures of propellants, extreme temperature cycling, long term permeability and requirements for damage tolerance.
Previous attempts at fabricating composite cryogenic pressure vessels have employed either a perforated honeycomb sandwich, a foam sandwich, or a laminated fluted sandwich. Laminated fluted designs had a number of disadvantages, including the need to use relative thick walls in order to carry the required compression and shear loads.
Honeycomb designs may also have various disadvantages, including their relatively heavy weight, and their reduced flatwise tensile strength and shear strength and impact resistance. Moreover, honeycomb designs rely on core-to-laminate bonds whose quality may not be nondestructively ascertained, and may be more difficult to tailor to particular shapes. Finally, over time, volatile fuels may permeate through the inner facesheet into the area between the cell walls. During launch or re-entry, as temperatures increase, permeated volatiles trapped within the core may begin to pressurize. In order to reduce the pressure build-up, others have proposed to perforate or slot the cell walls which allow excess gaseous build-up to be purged by circulating dry air or an inert gas through the sandwich panel. Perforation of the core cell walls in this manner, however, may reduce the shear, compression and bending strength of the panel.
Accordingly, there is a need for an improved panel design that overcomes the problems discussed above that may be tailored to produce components such as fuel tanks having a variety of shapes.